1. Field of the Invention
This invention pertains to motors and, in particular to external-rotor type drum motors.
2. Description of the Prior Art
German Offenlegungsschrift 1,448,383 discloses an external-rotor type drum motor in which a drum jacket of steel is drawn around the rotor and serves at the same time as the return yoke of the rotor. The advantage of the aforesaid type of drum motor is that the customary rotor laminations become unnecessary, thereby resulting in a substantial savings in electrical sheet material. Moreover, in the case of drum motors of such type which are permanent-magnet-excited, a significant amount of magnetic material can be accommodated with the same outside diameter as in prior motor constructions.
In the above discussed drum motor, the end bells of the motor are centered and fastened at shoulders of the drum jacket. This presents a disadvantage in that, if it is necessary to exchange or rework the drum, the external rotor must be dismantled completely and must also be centrifuged and balanced when returned to a completely assembled condition.
It is an object of the present invention to provide an external-rotor type drum motor which does not suffer from the aforesaid disadvantage.